This invention relates to an apparatus for rotating a drum and more particularly the invention relates to an apparatus for connecting a drive gear to the shell of a rotating drum. Specifically, the apparatus of the present invention is designed for rotating a large, heated rotary drum, such as a rotary kiln or dryer for thermal processing particulate material such as cement raw meal, limestone or the like.
Prior to the present invention, it was generally known that large rotary drums or cylindrical vessels such as rotary kilns, dryers, ball mills and the like would be rotatably mounted on suitable support mechanisms such as journals for ball mills and tires and roller support mechanisms in the case of large rotary kilns and dryers. Such drums are rotated by means of large girth gears which are concentrically mounted around the circumference of the drum and driven by a driving gear, such as a pinion which is connected through suitable reducers to a drive motor.
Suitable means must be provided for securing the girth gear to the cylindrical vessel so that the rotary motion of the gear is transmitted to the vessel to enable the vessel to be rotated. Because these rotary kilns and vessels are utilized for thermal processing material at temperatures up to 2000.degree. F. and more, even though the vessels may be lined with refractory material, the rotary vessel itself is exposed to high temperatures and may have skin temperatures on the order of 300.degree. to 500.degree. F. Since these vessels may be ten to eighteen feet in diameter and have a length of 200 feet and more, the high temperature can result in substantial thermal expansion of the rotary drum. In addition, the vessels may be slightly out of round during the loaded condition. As a result of the thermal expansion of the rotary drum or the slightly out of roundness of the vessel, it is necessary that the means for securing the girth gear to the rotary vessel allow for some misalignment of the vessel and allow for thermal expansion and contraction of the vessel relative to the girth gear.
Prior to the present invention various techniques have been utilized for securing the girth gear to the vessel. Included among these techniques are the use of tangential springs which are welded to the drum and attached to the girth gear through pivotal fasteners. This type of arrangement can be difficult to set up for initial installation of the gear.
Another technique used to connect the vessel to the girth gear includes the use of a flange mounted on the end of the vessel. With the flange welded to the vessel, a gear or other driving member is secured to the flange. This flange will have a shape such that heat from the vessel is transferred to the flange, but the expansion of the flange will be unable to move the gear resulting in stresses being applied to the vessel. These thermal stresses will create a loosening of refractory material which may line the inside of the vessel requiring a shut-down of the apparatus for replacement of refractory.